1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * kernel/crash_dump.c - Memory preserving reboot related code.
4 *
5 * Created by: Simon Horman <horms@verge.net.au>
6 * Original code moved from kernel/crash.c
7 * Original code comment copied from the i386 version of this file
8 */
9
10 #include <linux/errno.h>
11 #include <linux/types.h>
12 #include <linux/crash_dump.h>
13
14 #include <asm/page.h>
15 #include <linux/uaccess.h>
16
17 /**
18 * copy_oldmem_page - copy one page from "oldmem"
19 * @pfn: page frame number to be copied
20 * @buf: target memory address for the copy; this can be in kernel address
21 * space or user address space (see @userbuf)
22 * @csize: number of bytes to copy
23 * @offset: offset in bytes into the page (based on pfn) to begin the copy
24 * @userbuf: if set, @buf is in user address space, use copy_to_user(),
25 * otherwise @buf is in kernel address space, use memcpy().
26 *
27 * Copy a page from "oldmem". For this page, there is no pte mapped
28 * in the current kernel. We stitch up a pte, similar to kmap_atomic.
29 *
30 * Calling copy_to_user() in atomic context is not desirable. Hence first
31 * copying the data to a pre-allocated kernel page and then copying to user
32 * space in non-atomic context.
33 */
34 ssize_t
35 copy_oldmem_page(unsigned long pfn, char *buf,
36 size_t csize, unsigned long offset, int userbuf)
37 {
38 void *vaddr;
39
40 if (!csize)
41 return 0;
42 vaddr = __va(pfn<<PAGE_SHIFT);
43 if (userbuf) {
44 if (copy_to_user(buf, (vaddr + offset), csize)) {
45 return -EFAULT;
46 }
47 } else
48 memcpy(buf, (vaddr + offset), csize);
49 return csize;
50 }
51